Insulin receptors (IRs) and insulin signaling proteins are widely distributed throughout the central nervous system (CNS). To study the physiological role of insulin signaling in the brain, we created mice with a neuron-specific disruption of the IR gene (NIRKO mice). Inactivation of the IR had no impact on brain development or neuronal survival. However, female NIRKO mice showed increased food intake, and both male and female mice developed diet-sensitive obesity with increases in body fat and plasma leptin levels, mild insulin resistance, elevated plasma insulin levels, and hypertriglyceridemia. NIRKO mice also exhibited impaired spermatogenesis and ovarian follicle maturation because of hypothalamic dysregulation of luteinizing hormone. Thus, IR signaling in the CNS plays an important role in regulation of energy disposal, fuel metabolism, and reproduction.

Muscarinic acetylcholine receptors (mAChRs), M(1)-M(5), regulate the activity of numerous fundamental central and peripheral functions. The lack of small-molecule ligands that can block or activate specific mAChR subtypes with high selectivity has remained a major obstacle in defining the roles of the individual receptor subtypes and in the development of novel muscarinic drugs. Recently, phenotypic analysis of mutant mouse strains deficient in each of the five mAChR subtypes has led to a wealth of new information regarding the physiological roles of the individual receptor subtypes. Importantly, these studies have identified specific mAChR-regulated pathways as potentially novel targets for the treatment of various important disorders including Alzheimer's disease, schizophrenia, pain, obesity and diabetes.

Impaired functioning of pancreatic ␤ cells is a key hallmark of type 2 diabetes. ␤ cell function is modulated by the actions of different classes of heterotrimeric G proteins. The functional consequences of activating specific ␤ cell G protein signaling pathways in vivo are not well understood at present, primarily due to the fact that ␤ cell G protein-coupled receptors (GPCRs) are also expressed by many other tissues. To circumvent these difficulties, we developed a chemicalgenetic approach that allows for the conditional and selective activation of specific ␤ cell G proteins in intact animals. Specifically, we created two lines of transgenic mice each of which expressed a specific designer GPCR in ␤ cells only. Importantly, the two designer receptors differed in their G protein-coupling properties (Gq/11 versus Gs). They were unable to bind endogenous ligand(s), but could be efficiently activated by an otherwise pharmacologically inert compound (clozapine-N-oxide), leading to the conditional activation of either ␤ cell Gq/11 or Gs G proteins. Here we report the findings that conditional and selective activation of ␤ cell Gq/11 signaling in vivo leads to striking increases in both first-and second-phase insulin release, greatly improved glucose tolerance in obese, insulin-resistant mice, and elevated ␤ cell mass, associated with pathway-specific alterations in islet gene expression levels. Selective stimulation of ␤ cell Gs triggered qualitatively similar in vivo metabolic effects. Thus, this developed chemical-genetic strategy represents a powerful approach to study G protein regulation of ␤ cell function in vivo.beta cells ͉ G protein-coupled receptors ͉ transgenic mice ͉ type 2 diabetes T ype 2 diabetes has emerged as one of the major threats to human health in the 21st century (1). Impaired function of pancreatic ␤ cells is one of the key hallmarks of type 2 diabetes, and therapies targeted at improving ␤ cell function are predicted to offer considerable therapeutic benefit (2).␤ Cell function is modulated by the actions of different classes of heterotrimeric G proteins which are the immediate downstream targets of a multitude of G protein-coupled receptors (GPCRs). Like most other cell types, pancreatic ␤ cells are predicted to express many different GPCRs (3-5). Several lines of evidence suggest that activation of G s -coupled receptors expressed by pancreatic ␤ cells, including the glucagon-like peptide (GLP-1) receptor, improves ␤ cell function and can increase in ␤ cell mass via cAMP-dependent mechanisms (5-7). Pancreatic ␤ cells also express several G q/11 -coupled receptors, including the M 3 muscarinic acetylcholine (ACh) receptor (M3R) and GPR40, which can promote insulin release in an agonist-dependent fashion [for recent reviews, see (5,8)].Studies with GLP-1 receptor agonists have yielded detailed information about the beneficial effects of G s signaling on ␤ cell function and whole body glucose homeostasis (note that the GLP-1 receptor is enriched in pancreatic ␤ cells) (5-7). In contrast, much...

The muscarinic acetylcholine receptors are a subfamily of G protein-coupled receptors that regulate numerous fundamental functions of the central and peripheral nervous system. The past few years have witnessed unprecedented new insights into muscarinic receptor physiology pharmacology and structure. These advances include the first structural views of muscarinic receptors in both inactive and active conformations, as well as a better understanding of the molecular underpinnings of muscarinic receptor regulation by allosteric modulators. These recent findings should facilitate the development of new muscarinic receptor subtype-selective ligands that could prove to be useful for the treatment of many severe pathophysiological conditions.